1. Field of the Invention
This invention relates to a uniaxial horizontal sensor having a liquid and a bubble sealed inside a vessel for ascertaining levelness by detecting the position of the sealed bubble by means of an electrical signal, and is used in automatic leveling of machines and devices and in leveling devices, angle gauges, surveying instruments, measuring instruments, aircraft, ships, railway cars, automobiles and other applications where highly accurate levelness is required.
2. Description of the Prior Art
Known uniaxial horizontal sensors of this kind include:
1) those of a construction wherein as shown in FIG. 5 a glass pipe (g) is made in a shape curved in one axial direction, a common electrode plate (h) is disposed in a lower central position and opposite electrode plates (i) are disposed in two locations left-right symmetrically removed from the upper center and an electrolyte (j) with a large surface tension and a bubble (k) are so sealed inside the glass pipe (g) that in a range over which angle can be measured a part of each of the opposite electrode plates (i) makes contact with the bubble (k);
2) those of a construction wherein in a uniaxial inclination bubble pipe the position of the bubble is detected optically;
3) those of a construction wherein using a differential transformer an inductance balance change is detected; and
4) those of a construction wherein an output signal corresponding to the size of an electrostatic capacity is inputted into an arithmetic circuit and converted into a vessel inclination and angle (for example Japanese Unexamined Patent Publication No. H.3-142315).
The uniaxial horizontal sensor of 1) above is for the purpose of inclination angle zero horizontal attitude control, but because the degree of contact of the electrode plates with respect to the electrolyte is small, not only is there an influence on repeatability (repeat accuracy, hysteresis, etc.) but as a result of the construction using a glass pipe slight inclinations other than. in the axial direction to be measured, changes in the amount of contact of the electrolyte with the electrode plates due to expansion and contraction of the electrolyte caused by changes in the surrounding temperature of the sensor, and instability of the contact surfaces caused by the surface tension of the electrolyte become causes of accuracy errors and errors of reproducibility, and also because the surface tension of the electrolyte is large the response speed is slow and there is a risk of a phenomenon of the bubble breaking up as a result of vibration or the like occurring and causing large errors, and furthermore the structure makes mounting difficult, and for such reasons there has been the problem that it cannot be used as a sensor for securing high accuracy.
In the case of the uniaxial horizontal sensor of 2) above there is an influence of errors caused by deformation of the shape of the bubble due to temperature change and optical sensor errors because it depends on an optical sensor, and the sensors of 3) and 4) also have had the problem to be solved that similarly their degree of dependence on outside detecting devices is high and factors causing errors are large.